Formation consolidation using a combustible liner



T. c. vos'r, JR 3,414,055 FORMATION CONSOLIDATION USING A COMBUSTIBLE LINER Dec. 3, 1968 2 Sheets-Sheet 1 Filed Oct. 24, 1966 FIG.!

FIG. 7 FIG. 6

THOMAS c. VO'GT,JR.

INVENTOR ATTORNEY United States Patent 3,414,055 FORMATION CONSOLIDATION USING A COMBUSTIBLE LINER Thomas C. Vogt, Jr., Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Oct. 24, 1966, Ser. No. 589,107 18 Claims. (Cl. 16612) ABSTRACT OF THE DISCLOSURE A method of consolidating an incompetent formation wherein a liner of combustible material is positioned in a well at a point contiguous to the formation and then ignited to heat the formation to a temperature sufficient to consolidate the formation. A gas containing oxygen is supplied to the liner during combustion of the liner and is preferably supplied at a pressure sufficient to establish a positive pressure gradient in the well so that gas will continuously pass into the formation during the consolidation process to maintain permeability in the formation. In another embodiment of the invention, a pack of unconsolidated, particulate material is disposed about the liner in the well and is consolidated by the heat from the combustion of the liner.

Background 0 f the invention This invention relates to the consolidation of subterranean formations and, more particularly, to a method of applying heat to an incompetent formation in order to effect consolidation of the same.

Many problems are encountered in operating wells completed in so'called incompetent or unconsolidated formations. In such wells sand or other detrital material may flow into the well along with the produced formation fluids such as oil, gas, water, or mixtures thereof. The presence of such detrital material may result in undesirable accumulations thereof in the wells and also may cause difficulty in producing the fluids from the wells and in handling the produced fluids at the surface. Also, the presence of sand or other detrital material may lead to erosion of downhole producing equipment such as tubing strings. This problem is particularly serious in gas wells in which the gas enters the well under a high velocity. The sand grains entrained therein often produce substantial erosion of the adjacent downhole production equipment.

To overcome these problems various techniques have been developed in order to inhibit the flow of detrital material into a well along with the formation fluids. One conventional technique involves the provision of a gravel pack around the well bore which acts as a filter and prevents production of formation sand. This technique leaves much to be desired because of the expense and effort required in installing the gravel pack. Also, difficulties often are encountered in removing the gravel pack when it is desired to recomplete or otherwise work over the well. More recent practices involve the utilization of a naturally-occurring or injected substance which is responsive to heating at some specified temperature to effect the consolidation of the formation. For example, a bonding material such as a thermo-setting resin may be injected into a formation and thereafter heated in order too cure the resin and thereby effect consolidation of the formation. Another practice involves the heating of a naturallyoccurring or injected petroleum at a temperature sufficient to cause coking thereof such that the coke residue binds together the sand particles of the formation.

Various procedures have been proposed heretofore for heating in-situ such consolidating substances. One technique involves the use of a heating fluid such as a hot 3,414,055 Patented Dec. 3, 1968 inert gas which is injected through the well and into the formation. Other practices involve the use of downhole heating devices, such as electric or gas heaters. One serious shortcoming of such procedures is that they oftentimes result in uneven heating of the formation. For example, in the injection of a hot gas into the well, the gas many times will preferentially flow into zones of the formation of relatively high permeability. This may result in the occurrence of so-called hot spots at the face of the formation where high permeability zones exist with the attendant occurrence of cold spots between these zones.

Summary of the invention In accordance with the prevent invention, there is provided a new and improved method of heating the formation adjacent a well in order to effect consolidation thereof. The invention provides for the relatively even heating of the formation and produces other advantageous results as will appear hereinafter.

The invention is employed in a well penerating an unconsolidated formation, which formation includes a material responsive to heating at a specified temperature to effect consolidation of the formation adjacent to the well. The material may occur naturally in the formation or may be injected as will appear hereinafter. In carrying out the invention, a liner formed of a suitable combustible material is disposed within the well contiguous to an interval of the formation. Thereafter, the liner is subjected to combustion in order to heat the adjacent portion of the formation to at least the aforementioned specified temperature necessary to effect consolidation of the formation.

In one embodiment of the invention the liner comprises a plurality of perforations whereby the exposed surface area of the liner is increased, thus facilitating combustion of the liner. Preferably, a positive pressure gradient is maintained across the perforations during at least a portion of the time that the liner is undergoing combustion in order to effect the flow of gas through the perforations and into the formation. This results in an even more effective transfer of heat to the formation and also helps maintain the permeability of the formation during the heating process.

In another embodiment of the invention an expansible liner is utilized. This liner is inserted into the well in a collapsed condition and thereafter expanded prior to combustion thereof. Thus, the liner is placed in close proximity to the face of the formation within. the well, further increasing the effective transfer of heat to the formation.

In yet another embodiment of the invention a pack of unconsolidated particulate material is disposed about the liner within the space defined by the outer surface of the liner and the face of the formation. The pack includes a suitable bonding material or is otherwise responsive to being heated at a specified temperature to effect consolidation of the particulate material. Thereafter, the liner is subjected to combustion in order to effect consolidation of the pack. It is preferred in carrying out this embodiment of the invention to provide within the pack a suitable gas-forming substance which evolves gas in response to being heated to temperatures reached during combustion of the liner. Thus, gas is produced within the pack during the heating thereof and tends to preserve the permeability of the pack. Also, in carrying out this embodiment of the invention it is preferred to utilize a liner comprised of an outer sleeve of combustible material and an inner sleeve of a suitable refractory material. Thus, as the outer sleeve is consumed by combustion the inner sleeve remains to provide support for the particu- 0 late pack.

For a better understanding of the present invention,

reference may be had to the following detailed description taken in conjunction with the accompanying drawings, in which:

Brief description of the drawings FIGURE 1 is an illustration, partly in section, of a well in which one embodiment of the instant invention is car ried out;

FIGURE 2 is an illustration in section showing one form of liner utilized in carrying out the present invention;

FIGURE 3 is a side elevation showing another form of liner utilized in carrying out the invention;

FIGURE 4 is an illustration, partly in section, of a well in which the invention is carried out utilizing the liner shown in FIGURE 3;

FIGURE 5 is an illustration, partly in section, showing a well in which another embodiment of the invention is carried out;

FIGURE 6 is an illustration, partly in section, of a liner and envelope structure preferred for use in carrying out the embodiment of the invention of FIGURE 5; and FIGURE 7 is an illustration in section showing another form of liner structure.

Description of the preferred embodiments With reference to FIGURE 1, there is shown a wellbore v10 extending from the earths surface 12 and penetrating an unconsolidated subterranean formation 14. The formation 14 may be, for example, an unconsolidated sandstone containing oil and gas. The wellbore is provided with a casing 16 which may be cemented in a conventional manner to provide a cement sheath 18 interposed between the casing and the wall of the wellbore. As shown in the drawing, the casing 16 and surrounding cement sheath 18 may terminate at a point above the top of the formation 14. The well may be cased and cemented by any suitable technique. By way of example, the well may be cemented by the so-called port cementing technique. In this technique, a cementing basket (not shown) is provided around the casing adjacent the lower end thereof. After the casing and cementing basket are run into the well, cement then is pumped down the interior of the casing and into the annular space surrounding the casing through one or more ports or perforations in the casing located at a point above the cementing basket. Of course, the well may be completed by various other techniques as will be understood by those skilled in the art.

The well may be provided with a conventional packer 20 Which isolates the formation 14 from the upper portion of the well and a tubing string 21 which extends from the surface or wellhead 22 of the well through the packer. The tubing string is provided with a flowline 24 for the introduction or withdrawal of fluids. It is to be recognized that the well installation thus far described is exemplary only and that other suitable arrangements may be used which are consistent with the practice of the invention as hereinafter described,

In carrying out the present invention, a liner 26 formed of a suitable combustible material is disposed within the well contiguous with an interval of the formation 14 which is to be consolidated. While the liner 26 is shown as extending completely through the formation 14, it will be understood that the liner may be contiguous with respect to an interval less than the entire thickness of the formation. For example, where it is desired to consolidate only the upper portion of the formation 14 the liner may terminate at a point above the bottom of the formation 14.

As shown in FIGURE 1, the liner 26 is threadedly connected to the lower end of the casing string 16 at a suitable tool joint 27. Thus, the liner is inserted into the well with the casing. However, it will be understood that the liner may be disposed within the well by any appropriate procedure. For example, the liner may be inserted into the well subsequent to the setting and cementing of the casing by suitable wire line techniques. In this case,

the liner need not be supported from the casing, but instead may rest upon the bottom of the well or upon a packer disposed within the well.

The combustible material of which the liner is formed will depend upon the nature of the consolidating material in the formation. In a preferred embodiment of the invention described in greater detail hereinafter, the formation is heated to a temperature sufficient to cause some melting of sand grains within the formation, thus resulting in consolidation of the formation by fusion of the sand grains. This embodiment of the invention requires the development of relatively intense heat,

Thus, in carrying out this preferred embodiment of the invention, the liner may be formed of a metal such as iron which will react with molecular oxygen. The iron liner may be ignited by heating to a temperature on the order of 1710 F. in the presence of a sufllcient supply of oxygen. The oxygen may be injected through the tubing string 21 or may be present in the well as aluminum oxide, barium peroxide, etc. The iron will maintain self-sustained combustion at a temperature up to about 5900 F. (adiabatic reaction temperature) and will produce temperatures at the face of the formation on the order of about 3100 F. or more, depending upon the heat loss. The liner may be formed of other combustible materials depending upon the temperature requirement. For example, where it is desired to bring the formation up to about 4000 F. or above, the liner may be formed of magnesium which may be ignited at 1150 F. and has an adiabatic reaction temperature of about 6550 F.

The liner may be ignited by any suitable technique. For example, where an iron liner is used it may be ignited by means of an alumino-thermit process initiated by igniting a magnesium strip in barium peroxide placed in the bottom of the well. Alternatively, an ignition device such as an acetylene torch may be lowered through the tubing 21 and utilized to ignite the liner and supply oxygen. Preferably, the liner will be ignited such that initial combustion occurs near its unsupported end. Thus, where the liner is suspended from the casing as shown in FIGURE 1, the liner 26 will be ignited near the lower end thereof. Alternatively, where the liner is supported on the bottom of the well, it should of course be ignited adjacent the upper end thereof.

During combustion of the liner a suitable combustionsupporting gas such as air may be injected through the tubing 21. Preferably, the liner is provided with a plurality of perforations such as slots 28 in order to increase the surface area of the liner and thus facilitate combustion thereof. It also is preferred to inject gas through tubing 21 at a pressure sufiicient to establish a positive pressure gradient across the perforations 28, i.e., a pressure within the liner greater than the pressure within the formation. Thus, gas flow through the perforations 28 and into the formation 14 will maintain the permeability of the formationduring the consolidating reaction. In addition, the flow of gas through the perforations will aid in the transfer of heat from the point of combustion of the liner to the face of the formation. As the combustion of the liner proceeds upwardly from the bottom portion thereof, the adjacent face of the formation is subjected to a relatively even amount of heat. This will facilitate a uniform consoliclation of the formation and avoid the occurrence of so-called cold spots which may result in unconsolidated sections of the well.

Turning now to FIGURE 2, there is shown a modified form of liner 29 which comprises a plurality of sleeves 30, 32 and 34 disposed in a spaced, nested relationship with respect to one another. The sleeves 30, 32 and 34 are spaced from one another and secured together by means of spacing elements such as indicated by reference numeral 36. The liner of FIGURE 2 is particularly advantageous where it is desired to develop an intense heat as in the consolidation of the formation by fusion of sand grains therein. The construction of the liner shown in FIGURE 2 enables the provision of a relatively great amount of combustible material adjacent the formation face and yet provides for a large surface area to facilitate combustion. Also, the liner shown in FIGURE 2 will result in some prolongation of the burning time, increasing the period during which heat is applied to the formation. Preferably, each of the sleeves 30, 32 and 34 is provided with a plurality of perforations such as indicated by reference numeral 38. The method of the instant invention may be carried out utilizing the liner shown in FIGURE 2 similarly as described above with reference to FIGURE 1. Thus, the liner 29 may be disposed within the well and thereafter ignited by any suitable means. An oxygencontaining gas then may be injected into the inner sleeve by means of a tubing string, as described above.

In accordance with yet another embodiment of the invention, heat is supplied to the formation by combustion of a liner which, after insertion in the well, is expanded in order to place it in close proximity to the face of the formation. A suitable form of such an expansible liner is shown in FIGURE 3. With reference to FIGURE 3, there is shown a liner which takes the form of a cylindrical sleeve having a plurality of longitudinal convolutions, as indicated by reference numeral 42. As will be apparent from an examination of FIGURE 3, the liner 40 may be expanded after insertion into the well by the application of a suitable internal force. The liner 40 preferably is provided with perforations (not shown) in order to obtain the advantages noted above.

The embodiment of the invention utilizing a liner such as that shown in FIGURE 3 will now be described with reference to FIGURE 4 in which like elements are indicated by the same reference numerals as used in FIGURE 1. In FIGURE 4 the liner 40 is shown in its expanded position in which it is in close proximity with the face of the formation 14. The liner 40 is inserted into the well in a collapsed condition by any suitable technique. For example, the liner may be lowered into the well on a wire line (prior to the insertion of tubing 21 and packer 20) and thereafter expanded by means of a suitable expansion device. For example, such a device may comprise an inflatable bag which is carried within the liner and thereafter enlarged through the application of fluid pressure. Also, the liner 40 may be run into the well on a tubing string and thereafter expanded by means of a packer positioned within the liner. After the liner 40 is positioned as shown in FIGURE 4, combustion thereof may be carried out similarly as described above with reference to FIG- URE 1. In the embodiment of FIGURE 4, it will be recognized that by virtue of the close proximity of the liner to the face of the formation, the transfer of heat to the formation is enhanced.

In a further embodiment of the invention, a pack of unconsolidated particulate material is disposed about a liner and thereafter subjected to heat by combustion of the liner in order to consolidate the particulate material. This embodiment of the invention will be described with reference to FIGURE 5 in which like elements are designated by the same reference numerals as used in FIG- URES 1 and 4. More particularly, there is shown in FIGURE 5 a pack 48 of particulate material surrounding a combustible liner 50. The pack is responsive to being heated at a specified temperature to effect consolidation of the particulate material. For example, the pack 48 may comprise a mixture of unconsolidated sand which may be heated by combustion of the liner 50 to a temperature sufficient to cause fusion of the sand grains. In a preferred embodiment of the invention the pack 48 comprises, in addition to the particulate material which is consolidated, a suitable gas-forming substance which evolves gas during heating of the pack. In this embodiment of the invention, the gas produced during the heating step diffuses through the pack during consolidation thereof and tends to preserve the permeability of the pack. In addition, it is preferred to provide the liner 50 with perforations such as indicated by reference numeral 51 and to establish a positive pressure gradient across the perforations in order to ensure that a permeable consolidated pack is formed. The gas-forming substance may be of any suitable material which evolves gas at temperatures reached during the heating step. By way of example, the gas-forming material may take the form of calcium carbonate which decomposes at temperatures of about 1520 F. and above to evolve carbon dioxide. Thus, in carrying out this embodiment of the invention, the pack 48 may be comprised of a mixture of unconsolidated sand grains and particles of calcium carbonate. The liner 50 may be formed of iron which, as described above, produces temperatures on the order of 3100 F. and greater during combustion.

The pack of particulate material may include a bonding material in addition to the sand or other particulate material. For example, the pack 48 may include a glazing substance such as described in U.S. Patent No. 2,771,952 to Simm. The presence of such glazing substance will enable consolidation of the pack to proceed at a relatively low temperature, e.g., on the order of about l20 0 F.

The pack 48 of unconsolidated particulate material may be supplied to the annular space defined by the outer surface of the liner 50 and the face of the formation by any suitable technique. For example, conventional gravel packing practices in which the particulate material is suspended within a circulating fluid may be employed. It is preferred, however, to lower the pack into the well with the liner by attaching to the liner an envelope containing the particulate material comprising the pack. The envelope is formed of a suitable material which burns or otherwise decomposes at a temperature lower than the temperature at which consolidation of the pack occurs. Thus, the decomposition of the envelope during the early stages of heating allows the particulate material to fill the space between the liner and the face of the formation.

A suitable liner structure for carrying out this embodiment of the invention is illustrated in FIGURE 6. As shown in FIGURE 6, a liner 52 formed of suitable combustible material is surrounded by an envelope 54 which is secured thereto and within which is contained a pack 56 of particulate material. The envelope 54 may be formed of a material such as cotton such that the envelope decomposes as combustion of the liner is initiated. Thus, the particulate material will be freed from restraint by the envelope and will fall into place surrounding the liner 52.

In carrying out the invention and in particular the embodiment described above with reference to FIGURE 5, total combustion of the liner may under some circumstances result in some of the particulate material falling into the well before consolidation of such particulate material is completed. In order to guard against this occurrence, the invention preferably is carried out utilizing a liner, a portion of which is non-combustible under the conditions prevailing within the well so as to provide for continuous support of the particulate material. More particularly and with reference to FIGURE 7, there is shown a liner 60 which comprises an outer sleeve 62 formed of a suitable combustible material and an inner sleeve 64 formed of a suitable refractory material. For example, the inner and outer sleeves may be formed of magnesia and iron, respectively. The inner and outer sleeves are disposed in a nesting relationship with respect to one another and may form a laminated structure as shown in FIGURE 7. Alternatively, the sleeves may be spaced from one another similarly as shown in FIGURE 2 in order to provide for an increased surface area of the outer combustible sleeve or sleeves. In any case, the inner sleeve 64 is provided with perforations as indicated by reference numeral 66. Also, the outer sleeve 62 preferably is provided with perforations (not shown).

The liner 60 is disposed in the well and surrounded with a pack of particulate material, similarly as described above with respect to FIGURE 5. Thereafter, the liner is ignited and a positive pressure gradient is maintained across the perforations 66 and the perforations in the outer sleeve 62 in order to maintain gas flow through the pack of particulate material. Such gas How, in addition to maintaining the permeability of the pack and enhancing the transfer of heat to the pack, will tend to keep the perforations 66 clear of any particulate material during the consolidating action. From an examination of FIGURE 7, it will be recognized that as the outer sleeve 62 is consumed by combustion, the inner sleeve 64 will remain to provide for continuous support of the particulate material until the consolidation reaction is completed.

From the foregoing description, it will be recognized that by the instant invention intense heat may be developed in close proximity to the formation face, which heat is effectively and evenly transferred to the formation. Thus the formation adjacent the well may be heated expeditiously to unusually high temperatures.

As indicated previously, these characteristics of the invention may be utilized to advantage in the stabilization of unconsolidated sandstones by heating such formations to a temperature suflicient to cause fusion of the sand grains. Thus, in a preferred embodiment of the invention, a sand-containing formation is heated to at least the melting point of sand, e.g., on the order of 3100 F. The resulting stabilized portion of the formation will remain unimpaired even though subsequently subjected to acids as in various formation treating processes or to heat as in thermal recovery techniques.

Having described specific embodiments of the instant invention, it will be understood that further modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.

What is claimed is:

1. In the treatment of an unconsolidated formation penetrated by a well, said formation including a material responsive to being heated at a specified temperature to effect consolidation of said formation, the method of consolidating said formation adjacent said well comprisdisposing a liner within said well contiguous to an interval of said formation, said liner having a length substantially equal to the interval of said formation which is to be consolidated and being comprised of combustible material which will produce a temperature at least equal to said specified temperature when burned in the presence of oxygen,

supplying oxygen to said liner after it is disposed within said well, and

burning substantially all of said combustible material of said liner to heat substantially the entire interval of said formation adjacent said liner to at least said specified temperature whereby said material in said formation is consolidated.

2. The method of claim 1 including the step of providing said liner with a plurality of perforations prior to burning said liner whereby the surface area of said liner is increased facilitating combustion thereof.

3. The method of claim 2 wherein said oxygen is supplied to said liner in gaseous form at a pressure greater than the pressure of said formation so that a positive pressure gradient is maintained across said perforation during at least a portion of the time said liner is undergoing combustion thereby forcing gas through said perforations to maintain permeability in said formation.

4. The method of claim 1 wherein said liner comprises a plurality of sleeves disposed in a spaced nesting relationship with one another.

5. The method of claim 1 wherein said liner comprises an outer sleeve formed of comubstible material and an inner sleeve formedof refractory material, said inner sleeve having a plurality of perforations therein.

6. In the treatment of an unconsolidated formation penetrated by a well, the method of consolidating said formation adjacent said well comprising:

(a) disposing liner of combustible material in said Well contiguous to an interval of said formation, said liner being smaller in cross section than the cross section of said well, whereby a space is defined by the outer surface of said liner and the face of said formation in said well, said combustible material capable of producing a specified temperature when burned in the presence of oxygen,

(b) disposing within said space a pack of unconsolidated particulate material responsive to being heated at said specified temperature to effect consolidation of said particulate material,

(c) supplying oxygen to said liner, and

(d) burning said liner in the presence of oxygen to heat said pack to at least said specified temperature.

7. The method of claim 6 wherein said liner comprises a plurality of perforations whereby the surface area of said liner is increased facilitating combustion thereof.

8. The method of claim 7 wherein a positive pressure gradient is maintained across said perforations during at least a portion of the time said liner is undergoing combustion to force gas through said perforations to maintain permeability in said pack.

9. The method of claim 6 wherein said liner comprises an outer sleeve formed of combustible material and an inner sleeve formed of refractory material, said inner sleeve having a plurality of perforations therein.

10. The method of claim 6 in which said pack comprises unconsolidated sand and wherein said pack is heated in accordance with step (c) to a temperature of at least the melting point of said sand whereby a zone of fused sand is created within said pack.

11. The method of claim 6 wherein said pack includes a gas-forming substance which evolves gas during heating of said pack in accordance with step (c), said gas diffusing through said pack to preserve the permeability thereof during consolidation.

12. The method of claim 6 wherein said pack is disposed in said well in an envelope secured to said liner, said envelope being responsive to heating at a temperature less than said specified temperature to free said pack, whereby said particulate material falls into place around said liner.

13. In the treatment of an unconsolidated formation penetrated by a well, said formation including a material responsive to being heated at a specified temperature to effect consolidation of said formation, the method of consolidating said formation adjacent said well comprising:

disposing an expansible liner comprised of combustible material within said well contiguous to an interval of said formation while said liner is in a collapsed mode, said combustible material capable of producing a temperature at least equal to said specified temperature when burned in the presence of oxygen,

expanding said liner after it is disposed in said well,

supplying oxygen to said liner, and

burning said liner to heat said formation adjacent said liner to at least said specified temperature.

14. A method of consolidating an interval of particulate material in a well, said particulate material being responsive to heat at a specified temperature to effect consolidation of said particulate material, said method comprising:

disposing a liner within said well adjacent to said particulate material, said liner having a length substantially equal to that of said interval of particulate material to be consolidated and being comprised of a combustible material which Will produce a temperature at least equal to said specified temperature when burned in the presence of oxygen,

supplying oxygen to said liner after it is disposed Within said Well, and

burning substantially all of said combustible material of said liner to heat said particulate material to said 9 specified temperature whereby said particulate material is consolidated.

15. The method of claim 14 wherein said particulate material forms part of an incompetent formation Within the well.

16. The method of claim 14 wherein said particulate material is disposed in the Well about said liner prior to the burning of said liner.

17. The method of claim 14 wherein said particulate material is disposed in the well simultaneously with said liner.

18. The method of claim 14 wherein the step of supplying oxygen to said liner comprises:

disposing material adjacent to said liner which produces oxygen when burned with said liner.

10 References Cited UNITED STATES PATENTS 1,361,282 12/1920 Nolan 166-25 2,500,990 3/1950 Higginbotham et al. 166-58 2,650,539 9/1953 Greene 166-58 X 2,771,952 11/1956 Simm 166-39 X 3,003,555 10/1961 Freeman et a1 166-39 X 3,163,218 12/1964 Allen et al. 166-25 3,172,468 3/1965 Watson et a1. 166-25 3,280,911 10/1966 Strange et a1 166-228 JAMES A. LEPPINK, Primary Examiner. I. A. CALVERT, Assistant Examinern 

